Conventional frictions material is used, for example, for a clutch facing of a clutch disc which is generally manufactured by impregnating phenolic resin as a binding agent to a non woven fabric, and then heating and pressing them. However, in case that the conventional clutch is used immediately after manufacture, whole friction surface is not always pressed on a pressure plate or a flywheel, so that desired friction coefficient .mu., denoted by a curve Y of FIG. 3, can not be obtained under the initial condition of use. Therefore, in the conventional manufacturing process of clutch facing, a troublesome method such as resin coating on the friction surface must be carried out in order to obtain desired friction coefficient under the initial condition of use.
Furthermore, as shown in FIG. 4, outer periphery of a friction surface 101 of a pressure plate 100 may slightly inclines to a flywheel 102 in order to obtain a large transmission torque. Since outer periphery of the pressure plate 100 contacts partially with outer periphery of a friction surface 104 of a clutch facing 103 in this case, only outer periphery of the friction surface 104 is worn out exclusively as shown by a two-dot chain line D of FIG. 4, so that rust is produced thereat to induce troubles such as a decrease in a friction coefficient etc.
In order to enhance the effect to prevent the rust, a structure comprising thin-layer rust-preventive material, consists of a mixture which is including a caking material mainly composed of zinc or cadmium, is coated on a friction surface of friction material which is pressing on a surface of oppenent friction material so as to transfer the rust-preventive material to the surface of oppenent friction material (Japanese Patent Application No. 50-82207) has been proposed. Or a friction material comprising a friction material substrate, a flame sprayed metal which can be a sacrifical anode for iron on a surface of the substrate in an amount of 0.5 mg/cm.sup.2 to 8.0 mg/cm.sup.2 (U.S. Pat. No. 4,585,691), has also been proposed.
However, since an object of these structures is exclusively to obtain the effect to prevent the rust, they do not improve a friction coefficient of a friction material under the initial condition immediately after manufacuture. Futhermore, when the conventional friction materials are applied under the condition as illustrated in FIG. 4, their friction surface may peeled, so there is a difficulty to employ them.
This invention relates to an improvement in a friction material which is used under the condition mentioned above.
A main object of the present invention is to improve a friction coefficient of a friction material under the immediate situation after manufacture by forming a flame sprayed metal film on at least outer periphery of friction surface.
Further objects of the present invention are to enhance the effect to prevent the rust and to improve a durability of the material.